[Unbeliever]

Care to cite the FAR or AIM regulation for that?

No FAR/AIM reference because it doesn't exist. HOWEVER, there is a FAA safety circular about it. "Preventing Accidents During Aircraft Ground Operations"

No one should attempt to start an aircraft engine without a qualified person at the cockpit controls.

However, the NTSB, quotes that pamphlet on all hand propping accidents, and the FAA usually tries to pin a reckless charge based on that.

edit: Oh, and I think LoadStar mentioned that because Adam mentioned that as fact after demonstrating how to hand-prop a Citabria after Jaime failed to hand prop a Piper 6/Saratoga.

Edit #2: Hah! it is legal. 91.105 (a) During takeoff and landing, and while en route, each required flight crewmember shall—

(1) Be at the crewmember station unless the absence is necessary to perform duties in connection with the operation of the aircraft or in connection with physiological needs;

Even though it's not takeoff, I would imagine starting the aircraft is part of one's duties in connection of operation of the aircraft.

--Carlos V.